Session 3 Measuring Latitude and Longitude

We are located West of the Prime meridian and North of the Equator.

One minute of latitude is equal to one nautical mile. SCALE 090 N LATITUDE SCALE Latitude is measured from zero degrees at the equator to 90 degrees at the poles. In our area, the latitude scale, at the right or left-hand margin, increases from the bottom of our nautical charts toward the top. One minute of latitude is equal to one nautical mile. The latitude scales can be used to measure distance. The latitude scales are found at the left and right margins of a chart. 000 090 S

LONGITUDE SCALE Longitude is measured from zero at the prime meridian in Greenwich, UK, east and west to a point in the Pacific Ocean. In our area, the longitude scale, at the top or bottom margin, increases from right to left The Longitude Scales are located at the top and bottom of a nautical chart.. LONGITUDE SCALE

General Rules On a chart, LAT/LON is read in: Degrees Minutes Seconds Set your GPS to read out in this LAT/LON expression.

LAT/LON Expressions On a Nautical Chart: 042 deg 56 min 45 sec North 072 deg 45 min 25 sec West Typical GPS or LORAN read out: 042 56.750 N 072 45.417 W

Rules for reading LAT/LON On a Nautical Chart: Read the Degrees from the LAT/LON scales. Read the Minutes from the LAT/LON scales. Measure the Seconds.

Finding Your Latitude Position Longitude Scale Latitude Scale SMALL SCALE CHART Students should break out their charts and dividers to follow along Latitude goes up the side divided in one tenth of minute Longitude goes along the top and bottom Locate the White and Orange buoy “A” in the bottom left quadrant W Or ‘A’ Fl 4sec BELL

Measuring the Seconds of Latitude. Step ONE – Place one point of the dividers on the object or target. Step TWO - Stretch the other point of the dividers to nearest Parallel of Latitude. Step THREE - Without disturbing the opening, move the dividers to the Latitude scale in the left or right margins. 2 Spread dividers and put one point on object The nearest line is 41° 20’N You want to insure it is just touching the line Read off the longitude at the bottom Answer 3 Step FOUR - Read the seconds of latitude. 4 1

The LATITUDE SCALE on a Small Scale Chart usually depicts decimal minutes. The parallel line from the Bell. 11.0 min. 041 10.7” N Seconds 041 10’ 42” N 10.5 min Degrees 10.0 min. Minutes

One Minute of Latitude equals One Nautical Mile DISTANCE One Minute of Latitude equals One Nautical Mile

Sixty Seconds of Latitude equals One Nautical Mile DISTANCE Sixty Seconds of Latitude equals One Nautical Mile

6 seconds 1/10 of a Mile ONE NAUTICAL MILE The Second Scale on a Small Scale Chart 6 seconds 1/10 of a Mile SIXTY SECONDS OF LATITUDE ONE NAUTICAL MILE

Finding your Longitude Position Longitude Scale Latitude Scale SMALL SCALE CHART Students should break out their charts and dividers to follow along Latitude goes up the side divided in one tenth of minute Longitude goes along the top and bottom Locate the White and Orange buoy “A” in the bottom left quadrant W Or ‘A’ Fl 4sec BELL

Measuring the Seconds of Longitude Step ONE - Place one divider point on the object or target.. Step TWO - Stretch the other point of the dividers back to the nearest meridian of Longitude. 2 Step THREE - Without disturbing the opening, move the dividers to the Longitude Scale at the top or bottom margin. Spread dividers and put one point on object The nearest line is 071° 20’W You want to insure it is just touching the line Read off the longitude at the bottom Answer 1 3 Step FOUR - Read the seconds of Longitude. 4

The vertical line from the Bell. The Longitude Scale The vertical line from the Bell. Seconds Degrees Minutes 071 01.4’ W or 071 01’ 24” W

Any questions about how to read and plot Latitude and Longitude?